Salmon Sharks in Alaska
SALMON SHARKS
Salmon sharks (Lamna ditropis) are fish, in the Lamnidae family of sharks. This family includes the great white and mako sharks. Lamnidae sharks are warm-blooded (partially endothermic) and salmon sharks are the warmest of the Lamnidaes, as warm as
20ºF (7ºC) warmer than the waters in which they swim.
SIZE: Salmon sharks can grow to about 12 feet (3.7 m) and weigh over 1000 pounds (454 kg). Females are slightly larger than males.
COLOR: Salmon sharks are dark gray to nearly black above. The underside is whitish with gray blotches. The shark’s colorations help camouflage it both from above and below.
SPEED: Salmon sharks are well adapted to travel swiftly through the water. Their bodies are stocky with a pointed or conical snout. Salmon sharks use their large, powerful tail to propel them through the water. Another adaptation for speed is their rough skin. The skin holds water, creating a water-to-water low-resistance interface. When doing submarine research, the U.S. Navy became interested in how salmon sharks could travel so fast in water. Navy researchers reported clocking salmon sharks at over 50 miles per hour (80 km/hr), which puts them among the fastest of fish.
LONGEVITY: Most fish are aged using bony structures called otoliths; however, sharks do not have bones, making it difficult to age them. A recent discovery has found that the snout of the salmon shark is ossified, or bone. What appear to be annual rings in the snout’s bone indicate that a 6½-foot (2-m), 300-pound (136- kg) female salmon shark is about ten or eleven years old. From this information, researchers estimate that salmon sharks may live 25 years or more.
REPRODUCTION: Male salmon sharks become sexually mature at about five years and females at about eight to 12 years. Breeding takes place during the fall. Salmon sharks are ovoviviparous meaning that they produce eggs that hatch within the female’s body. During gestation the young sharks attack and consume non-developing eggs. This is common among sharks. The female, therefore, gives birth to two to five live young, called pups. The estimated gestation period is around nine months to a year. Young are 32–34 inches (81–86 cm) long at birth and are fully equipped with
sharp senses and sharp teeth, the better to take prey and avoid predators.
SOCIAL STRUCTURE: Salmon sharks feed together on schools of salmon and other fish and may work together to herd the prey. The sharks appear to be non-aggressive towards each other as they feed. During breeding, males will bite on to females to hold on. What appears to us to be dangerous and aggressive behavior seems to work for sharks. The sharks seem to not be troubled by pain.
DISTRIBUTION: Salmon sharks can be found in nearshore and offshore waters of the North Pacific Ocean, from Baja California to the Bering Sea and west to Russia, Korea and Japan.
MOVEMENTS AND MIGRATION: Satellite tags attached to salmon shark dorsal fins have revealed that in the summer some sharks migrate to near-shore waters in pursuit of prey. They tend to use deeper and more offshore waters after salmon spawning ends in October. Salmon sharks are highly migratory and may move thousands of miles (>10,000 km) each year in search of prey. Some of the salmon sharks in Prince William Sound, Alaska stay in these waters year round and feed on the large schools of herring. In Russia, salmon sharks are called herring sharks.
HABITAT: Salmon sharks can be found patrolling nearshore waters as they search for prey. However, they spend much of the year in the open ocean, often at great depths. During the summer, salmon sharks hunt near the thermocline, an area in the water column where there is an abrupt change in water temperatures.
PREY: Salmon sharks are opportunistic feeders. They consume a wide variety of prey including salmon, squid, rockfish, pollock, herring, capelin, sablefish, mackerel, sculpin, tomcod, daggerteeth, lantern fishes, pomfret, shrimp, lancet fish, spiny dogfish sharks, arrowtooth flounder and sea otters.
PREDATORS: Other sharks may prey upon salmon sharks and they are sometimes taken by orcas. It is not known if the transient type and/or resident type orcas are taking the sharks. Some commercial salmon fishermen regularly kill salmon sharks, and there is an active and growing sport fishery in Alaska for salmon sharks. Here a story about researching salmon sharks here: http://seagrant.uaf.edu/news/00ASJ/10.12.00_SharkInvasion.html.
Salmon sharks (Lamna ditropis) are fish, in the Lamnidae family of sharks. This family includes the great white and mako sharks. Lamnidae sharks are warm-blooded (partially endothermic) and salmon sharks are the warmest of the Lamnidaes, as warm as
20ºF (7ºC) warmer than the waters in which they swim.
SIZE: Salmon sharks can grow to about 12 feet (3.7 m) and weigh over 1000 pounds (454 kg). Females are slightly larger than males.
COLOR: Salmon sharks are dark gray to nearly black above. The underside is whitish with gray blotches. The shark’s colorations help camouflage it both from above and below.
SPEED: Salmon sharks are well adapted to travel swiftly through the water. Their bodies are stocky with a pointed or conical snout. Salmon sharks use their large, powerful tail to propel them through the water. Another adaptation for speed is their rough skin. The skin holds water, creating a water-to-water low-resistance interface. When doing submarine research, the U.S. Navy became interested in how salmon sharks could travel so fast in water. Navy researchers reported clocking salmon sharks at over 50 miles per hour (80 km/hr), which puts them among the fastest of fish.
LONGEVITY: Most fish are aged using bony structures called otoliths; however, sharks do not have bones, making it difficult to age them. A recent discovery has found that the snout of the salmon shark is ossified, or bone. What appear to be annual rings in the snout’s bone indicate that a 6½-foot (2-m), 300-pound (136- kg) female salmon shark is about ten or eleven years old. From this information, researchers estimate that salmon sharks may live 25 years or more.
REPRODUCTION: Male salmon sharks become sexually mature at about five years and females at about eight to 12 years. Breeding takes place during the fall. Salmon sharks are ovoviviparous meaning that they produce eggs that hatch within the female’s body. During gestation the young sharks attack and consume non-developing eggs. This is common among sharks. The female, therefore, gives birth to two to five live young, called pups. The estimated gestation period is around nine months to a year. Young are 32–34 inches (81–86 cm) long at birth and are fully equipped with
sharp senses and sharp teeth, the better to take prey and avoid predators.
SOCIAL STRUCTURE: Salmon sharks feed together on schools of salmon and other fish and may work together to herd the prey. The sharks appear to be non-aggressive towards each other as they feed. During breeding, males will bite on to females to hold on. What appears to us to be dangerous and aggressive behavior seems to work for sharks. The sharks seem to not be troubled by pain.
DISTRIBUTION: Salmon sharks can be found in nearshore and offshore waters of the North Pacific Ocean, from Baja California to the Bering Sea and west to Russia, Korea and Japan.
MOVEMENTS AND MIGRATION: Satellite tags attached to salmon shark dorsal fins have revealed that in the summer some sharks migrate to near-shore waters in pursuit of prey. They tend to use deeper and more offshore waters after salmon spawning ends in October. Salmon sharks are highly migratory and may move thousands of miles (>10,000 km) each year in search of prey. Some of the salmon sharks in Prince William Sound, Alaska stay in these waters year round and feed on the large schools of herring. In Russia, salmon sharks are called herring sharks.
HABITAT: Salmon sharks can be found patrolling nearshore waters as they search for prey. However, they spend much of the year in the open ocean, often at great depths. During the summer, salmon sharks hunt near the thermocline, an area in the water column where there is an abrupt change in water temperatures.
PREY: Salmon sharks are opportunistic feeders. They consume a wide variety of prey including salmon, squid, rockfish, pollock, herring, capelin, sablefish, mackerel, sculpin, tomcod, daggerteeth, lantern fishes, pomfret, shrimp, lancet fish, spiny dogfish sharks, arrowtooth flounder and sea otters.
PREDATORS: Other sharks may prey upon salmon sharks and they are sometimes taken by orcas. It is not known if the transient type and/or resident type orcas are taking the sharks. Some commercial salmon fishermen regularly kill salmon sharks, and there is an active and growing sport fishery in Alaska for salmon sharks. Here a story about researching salmon sharks here: http://seagrant.uaf.edu/news/00ASJ/10.12.00_SharkInvasion.html.
PREDATORY CHARACTERISTICS: Salmon sharks are equipped with good vision and sense of smell to aid in locating and attacking prey. Another well-developed sense is their ability to detect weak electromagnetic fields that are emitted by the muscles of swimming fish and other prey. Sharks have a number of large pores, or channels, in their snouts that are used to detect these weak electrical fields. Sharks’ “sixth sense” is so acute as to allow them to track their prey by following the wake the prey leaves in the water. Muscles work more efficiently when warm. Most fish lose their internal heat to the surrounding water. A salmon shark’s warm-bloodedness is achieved by countercurrent heat exchange in which heat produced by internal muscle activity is used to warm the oxygenated blood returning from the gills. Salmon
sharks benefit from warm-bloodedness and more efficient muscles by being able to reach higher swimming speeds. Salmon sharks also are equipped with several rows of moderately large, smooth-edged teeth. These are used to grasp and tear their prey into bite-sized pieces.
Much of the salmon shark’s prey is taken in deep water. However, some salmon sharks will move into shallow bays and the mouths of salmon streams to pursue salmon that are preparing to spawn. The sharks concentrate their efforts in these hot spots, and as many as 1,000 salmon sharks per square mile (386 salmon sharks per km2) have been observed in these areas. The sharks will hunt the salmon in groups, or packs, similar to how wolves hunt their prey. Salmon are attacked from below or behind. Salmon sharks have been seen leaping out of the water in pursuit of their prey and may clear the water with a salmon in their jaws.
At least two accounts of salmon sharks taking sea otters were reported in Prince William Sound, Alaska. In one account the 300–400 pound (136–181 kg) shark attacked a female otter as her pup swam nearby. The shark grabbed the sea otter and shook, tearing the otter to pieces only ten feet (3 m) from a fishing boat. Otter blood was splattered across the boat’s stern and onto the fishermen. The pup sea otter escaped, but likely died of starvation or was preyed upon by bald eagles, which are on the lookout for unattended young otters. I'm still not convinced these were not great white sharks taking the sea otters.
Salmon sharks are considered dangerous because of their large size and aggressive nature. However, they are rarely aggressive towards people, and there is only one account of a salmon shark attacking and biting a person. You can watch a video of a photographer taking video taken on a shark expedition in Prince William Sound of a salmon shark and the lack of aggression here (http://www.youtube.com/watch?v=9aS077MDJrg). But salmon sharks can be dangerous as described in this story: http://seagrant.uaf.edu/news/00ASJ/09.28.00_RiskyScience.html.
CURRENT STATUS: Japanese scientists estimate more than 2,000,000 salmon sharks hunt the North Pacific Ocean, but this estimate is controversial and may be high. Their population appears to be healthy in Alaska.
However, salmon sharks are a long-lived, slow-growing species with a low reproductive rate. This makes them susceptible to over-exploitation. Fisheries on sharks would likely result in a dramatic decline in the regional shark population, similar to what has occurred to other shark populations in other oceans. Alaska fisheries managers are taking a conservative management approach to shark fisheries. This probably has helped in maintaining healthy shark populations in Alaska and also a relatively stable marine ecosystem. The Alaska fisheries managers have not addressed as yet the many fishermen in the region who regularly kill any sharks they catch by cutting off their tails or shooting them on sight and bycatch of sharks in the Bering Sea..
ECOLOGY/CONSERVATION: Salmon sharks move into areas of high food abundance, or “hot spots.” They consume the schools of fish until the amount of prey is reduced or dispersed. Then the sharks move on to the next patch of food. Salmon sharks have learned where and when these hot spots occur. This behavior may result in salmon sharks intercepting salmon runs but they take far less than the number of fish harvested by fishermen.
An interesting thing about salmon shark predation in Alaskan waters is that it may afford some stability to the ecosystem. Mathematical models show that if a predator-control program removed these sharks from the ecosystem some marine species populations would decline. Scientists think it would work like this: If the sharks were removed, several fish species numbers would increase, especially arrowtooth flounder. The increased flounder population would remove smaller forage fish such as capelin and herring, which reduces the food supply for other fish, seabirds and marine mammals. Some marine mammal populations in the Gulf of Alaska are already at critically low numbers, so further declines would have a devastating effect on the ecosystem and likely would force more fishing restrictions to
protect the food of the marine mammals. The complexities of the predator–prey relationship and their effects on the marine ecosystem are difficult and next-to-impossible to predict and manage. A precautionary approach to fisheries and predator management is the wisest choice.
Publications:
Wright, Bruce A., 2011. Alaska Predators, Their Ecology and Conservation. Hancock House Publishing. 119 pages. http://www.hancockhouse.com/products/alapre.htm
Wright, Bruce. 2010. Salmon Swimming Against Multiple Threats. Science 19 March 2010. Vol. 327. No. 5972, p. 1452a.
Wright, Bruce. 2010. Predators Could Help Save Pollock. Science 5 February 2010: 642.
Okey, T.A., B.A. Wright and M. Brubaker. 2007. Climate change, trans-oceanic fisheries impacts, or just variability?: Salmon shark connections. Fish and Fisheries. Volume 8, Issue 4, Pages 359 – 366.
sharks benefit from warm-bloodedness and more efficient muscles by being able to reach higher swimming speeds. Salmon sharks also are equipped with several rows of moderately large, smooth-edged teeth. These are used to grasp and tear their prey into bite-sized pieces.
Much of the salmon shark’s prey is taken in deep water. However, some salmon sharks will move into shallow bays and the mouths of salmon streams to pursue salmon that are preparing to spawn. The sharks concentrate their efforts in these hot spots, and as many as 1,000 salmon sharks per square mile (386 salmon sharks per km2) have been observed in these areas. The sharks will hunt the salmon in groups, or packs, similar to how wolves hunt their prey. Salmon are attacked from below or behind. Salmon sharks have been seen leaping out of the water in pursuit of their prey and may clear the water with a salmon in their jaws.
At least two accounts of salmon sharks taking sea otters were reported in Prince William Sound, Alaska. In one account the 300–400 pound (136–181 kg) shark attacked a female otter as her pup swam nearby. The shark grabbed the sea otter and shook, tearing the otter to pieces only ten feet (3 m) from a fishing boat. Otter blood was splattered across the boat’s stern and onto the fishermen. The pup sea otter escaped, but likely died of starvation or was preyed upon by bald eagles, which are on the lookout for unattended young otters. I'm still not convinced these were not great white sharks taking the sea otters.
Salmon sharks are considered dangerous because of their large size and aggressive nature. However, they are rarely aggressive towards people, and there is only one account of a salmon shark attacking and biting a person. You can watch a video of a photographer taking video taken on a shark expedition in Prince William Sound of a salmon shark and the lack of aggression here (http://www.youtube.com/watch?v=9aS077MDJrg). But salmon sharks can be dangerous as described in this story: http://seagrant.uaf.edu/news/00ASJ/09.28.00_RiskyScience.html.
CURRENT STATUS: Japanese scientists estimate more than 2,000,000 salmon sharks hunt the North Pacific Ocean, but this estimate is controversial and may be high. Their population appears to be healthy in Alaska.
However, salmon sharks are a long-lived, slow-growing species with a low reproductive rate. This makes them susceptible to over-exploitation. Fisheries on sharks would likely result in a dramatic decline in the regional shark population, similar to what has occurred to other shark populations in other oceans. Alaska fisheries managers are taking a conservative management approach to shark fisheries. This probably has helped in maintaining healthy shark populations in Alaska and also a relatively stable marine ecosystem. The Alaska fisheries managers have not addressed as yet the many fishermen in the region who regularly kill any sharks they catch by cutting off their tails or shooting them on sight and bycatch of sharks in the Bering Sea..
ECOLOGY/CONSERVATION: Salmon sharks move into areas of high food abundance, or “hot spots.” They consume the schools of fish until the amount of prey is reduced or dispersed. Then the sharks move on to the next patch of food. Salmon sharks have learned where and when these hot spots occur. This behavior may result in salmon sharks intercepting salmon runs but they take far less than the number of fish harvested by fishermen.
An interesting thing about salmon shark predation in Alaskan waters is that it may afford some stability to the ecosystem. Mathematical models show that if a predator-control program removed these sharks from the ecosystem some marine species populations would decline. Scientists think it would work like this: If the sharks were removed, several fish species numbers would increase, especially arrowtooth flounder. The increased flounder population would remove smaller forage fish such as capelin and herring, which reduces the food supply for other fish, seabirds and marine mammals. Some marine mammal populations in the Gulf of Alaska are already at critically low numbers, so further declines would have a devastating effect on the ecosystem and likely would force more fishing restrictions to
protect the food of the marine mammals. The complexities of the predator–prey relationship and their effects on the marine ecosystem are difficult and next-to-impossible to predict and manage. A precautionary approach to fisheries and predator management is the wisest choice.
Publications:
Wright, Bruce A., 2011. Alaska Predators, Their Ecology and Conservation. Hancock House Publishing. 119 pages. http://www.hancockhouse.com/products/alapre.htm
Wright, Bruce. 2010. Salmon Swimming Against Multiple Threats. Science 19 March 2010. Vol. 327. No. 5972, p. 1452a.
Wright, Bruce. 2010. Predators Could Help Save Pollock. Science 5 February 2010: 642.
Okey, T.A., B.A. Wright and M. Brubaker. 2007. Climate change, trans-oceanic fisheries impacts, or just variability?: Salmon shark connections. Fish and Fisheries. Volume 8, Issue 4, Pages 359 – 366.
Salmon Shark Migration
Salmon sharks were once thought to be a local coastal species, but Bruce Wright hypothesized they were highly migratory based on observations of young salmon sharks becoming stranded on California beaches. Tagging sharks with satellite tracking tags has revealed their highly migratory behavior as they search prey concentrations in the North Pacific Ocean.
Other species:
Pacific sleeper sharks in Alaska
Great white sharks in Alaska
Bald Eagle
Gyrfalcon
Great Horned Owl
Snowy Owl
Black Bears
Brown Bears
Polar Bears
Orcas
Wolves
Wolverine
Other species:
Pacific sleeper sharks in Alaska
Great white sharks in Alaska
Bald Eagle
Gyrfalcon
Great Horned Owl
Snowy Owl
Black Bears
Brown Bears
Polar Bears
Orcas
Wolves
Wolverine